[TenTec] Fwd: OmniVI logic board work

[Glenn]

Hi Barry,


Good idea.. I will try to set up soon and make a recording, however, the limiting factor, is still
how well our ears/brains can decipher/separate two weak signals in the same passband, choosing one or the other signal.
My observations, SO FAR, were under lab conditions where the only RF getting to the front end of the transceivers was coming from two 
signal generators. I actually have 4) 8640B's in the lab all with recent cal stickers. 


The test I would like to perform is with two weak signals, less than S1 in the passband and an S 9 signal 2 KHz above then 2KHz below the passband.
My guess is the K3 may get the nod here due it's close in dynamic range. However, I know how bad the K3 resolves multiple signals close  together
at .1uv. I'll need to increase the output of the generators enough so that the K3 does clearly resolve/process the two signals. Whatever that turns out to be
is where I'll test the K3, Omni 6 and Corsair II.. BTW, i should have mentioned earlier, the Omni 6 I was testing with had the INRAD front end roofing filter and
all other filters were also INRAD. At some point, I would like to do the same test with all things being equal but with Ten Tec filters vs INRAD filters.


To many plans and not enough time... Hi


73,
Glenn WA4AOS
DSM Labs (dot com)



-----Original Message-----
From: Barry N1EU <barry.n1eu at gmail.com>
To: Discussion of Ten-Tec Equipment <tentec at contesting.com>
Sent: Thu, Sep 29, 2011 9:30 am
Subject: Re: [TenTec] Fwd: OmniVI logic board work


On Thu, Sep 29, 2011 at 12:59 PM, Glenn <wa4aos at aol.com> wrote:

> Case and point.  I can take two of my calibrated HP 8640B signal generators 
and set them both for .15 microvolts and separate the carriers by 75Hz.
> Then switching the output of one of the 8640B's OFF and ON rapidly using a 
shielded keying fixture, (see note below ) I built, I can clearly here both 
signals
> as defined dits and dahs.  Using the same arrangement on the K3 or Omni 7, the 
signals are poorly defined with digital artifacts making neither decent enough 
to
> make understand the dits and dahs. Leading and trailing edges of both signals 
are distorted and copy would be nearly impossible at those levels. The analog
> front ends in the O6 and Corsair  are difficult copy but you can make out what 
the keyer is sending.


Glenn, if you could make audio recordings of the test you described
showing good resolution by O6/Corsair and poor resolution by K3, you
would be making a huge contribution toward the 2-year old debate about
poor pileup readability on the K3.  I've often though that the O6
might make a better run radio (i.e. to handle pileups) than the K3.

Appreciate your comments on variability of O6 sensitivity because this
has also been my experience.  I've had 3 Omni 6/6+'s in the shack in
the past couple of months with vintages spanning 1992-2001 and the
oldest unit had the quietest/most sensitive front end.  If someone
could document the front end diode replacement (i.e., how to remove
the board, what diodes to use), they would be doing a real service to
the user community.  I understand it's a tough job and the pin diodes
commonly recommended for the O6 job are no longer available.

Just an aside, but I'm not a big fan of the O6 dsp circuit and my
initial efforts at bypassing it have yielded MUCH more pleasing audio,
although it remains a work in progress needing more of my time.

73,
Barry N1EU
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